The goal of this proposal is to identify proteins of BLV recognized by T-cell subpopulations and determine the contribution of these proteins to viral pathogenesis. Our hypothesis is that BLV pathogenesis is governed by the T-cell response. Preliminary studies presented in this application demonstrate the feasibility of in vitro translation of viral antigens for evaluating T-cell proliferation to viral proteins and peptides. Through use of increasingly shorter peptide fragments translated from cDNA transcripts, the peptide units recognized by the T- cells will be mapped within the protein. We postulate that as infection progresses to PL and tumor formation, the proficiency of T-cells to recognize selected BLV proteins either declines or expands and determines the viral pathogenic state. this approach provides the first opportunity to selectively address the importance of T-cell epitopes and particularly epitopes within Tax and Rex proteins known to be critically important for regulating cell transformation. Determining the T-cell repertoire to specific viral proteins during different disease states would address the importance of the animal to control viral latency or allow tumor progression. Lack of this information regarding BLV infection has hindered our understanding of lymphocyte regulation of BLV pathogenesis. We have developed the essential reagents necessary to determine the contribution of these different subpopulations of cells to the disease state within the natural host. Experiments are designed to address the following specific aims: 1) BLV viral proteins recognized by T-cells from cattle classified as seropositive, persistently lymphocytotic, or tumor bearing will be identified. 2) A panel of bovine T-cell lines responsive to individual BLV proteins will characterize the lymphocyte phenotypes and the T-cell cytokines produced. 3) Specific T-cell epitope locations within the Tax and Rex viral proteins will be mapped using cattle with different disease states. 4) The ability of cytotoxic T-cells to lyse autologous target cells transfected with individual BLV proteins will be determined from cattle in each disease state. Characterizing the interactive role of T-cell recognition required for controlling retroviral infection in host cells, which has never been precisely defined in HTLV or BLV retroviral infections, is the central goal of this application. These data could become immediately applicable in determining the role of T-cells in controlling or fostering viral pathogenesis in bovine cells. Also, these data would be informative for defining the relationship of the human cellular immune system and HTLV-I, whose viral genome is similarly arranged.